1. Field of the Invention
The present invention relates to a lithographic type diffusion transfer developing composition which is prepared by incorporating an amine compound or the derivative thereof in a diffusion transfer developing composition. The object of the invention is to directly prepare a half-tone photographic original plate having excellent half-tone dot quality with low fringe, by a positive-positive diffusion transfer development.
2. Description of the Prior Art
In the art of photographic plate-making the continuous gradation of an original must be converted to a half-tone dot gradation. According to standard processes commonly practiced at present a half-tone negative or half-tone positive photographic original plate comprising hard dots is prepared by covering an original having a continuous gradation with a screen, printing it on a high contrast lithographic type light-sensitive material and then subjecting it to a lithographic type development (this process is described in "Photographic Processing Chemistry", pp. 163-165, written by Mason and issued by Focal Press Limited in 1966).
However, in a process of conducting lithographic development using a lithographic light-sensitive material a positive original is converted to a half-tone negative while a negative original is converted to a half-tone positive. Such a process is a so-called negative-positive process, and hence a positive half-tone dot original plate cannot directly be prepared from a positive original or a negative half-tone dot original plate from a negative original. Accordingly, in the case of a positive-positive process an original must first be converted to an intermediate half-tone negative, which is then subjected to reversal.
It will be clear from the above discussion that the direct preparation of a half-tone dot photographic original plate from an original without preparing an intermediate negative would be advantageous from an economical viewpoint and serve to simplify such processing.